1. Field of the Invention
The present invention relates generally to the control of a hybrid electric vehicle, and more particularly to a method for controlling a wheel drive system of a hybrid electric vehicle.
2. Background Art
Previously, hybrid electric vehicles employed control strategies that restricted “shift-up” actions of an automatic transmission to reduce shifting shocks that occurred as power source output decreased. An example of such a control strategy is described in U.S. Pat. No. 5,982,045. However, these hybrid vehicle control strategies did not address the problems associated with executing a transmission downshift to a lower gear ratio while simultaneously starting a drive power source, such as an engine of the hybrid electric vehicle.